1. Field of the Invention
The present invention relates to a method and apparatus for reducing the hydrogen concentration in a silicon carbide film. More particularly, the present invention relates to a method and apparatus for reducing the concentration of hydrogen in silicon carbides film produced by plasma enhanced chemical vapor deposition.
2. Background of the Art
Silicon carbide (SiC) films are useful in the fabrication of integrated circuits and printer print heads to provide corrosion resistant and protective layers over structures formed thereon. Silicon carbide films can be deposited by physical vapor deposition (PVD) or chemical vapor deposition (CVD).
In physical vapor deposition, a target made of silicon carbide is located in a processing chamber opposite a substrate. A plasma is generated between the target and substrate by supplying an inert gas such as argon into the chamber and providing an electrical bias to the target and grounding the chamber walls and the support member. The plasma ionizes the argon gas and the ions bombard the surface of the target to sputter the target material which deposits onto the substrate. The composition of the resulting film is primarily determined by the composition of the target, therefore, PVD of silicon carbide provides films having very low concentrations of hydrogen incorporated therein. PVD of silicon carbide films, however, is typically a slow throughput.
CVD, while faster than PVD, typically requires decomposition of a film precursor or precursors including silicon and carbon sources which typically include hydrogen, thereby causing hydrogen to be incorporated into the film. Plasma-enhanced chemical vapor deposition (PECVD) is one process used in the manufacture of semiconductor devices for depositing SiC on various substrates. In PECVD of SiC, a substrate is placed in a vacuum deposition chamber equipped with a pair of parallel plate electrodes or other means of coupling electrical energy into the chamber, such as a helical coil. The substrate is generally mounted on a support member which is also the lower electrode. A flow of a reactant gas is provided in the deposition chamber through a gas inlet manifold which may also serve as the upper electrode. A radio frequency (RF) voltage is applied between the two electrodes to generate RF power sufficient to cause the reactant gas to form a plasma. The plasma causes the reactant gases to vigorously react and deposit a layer of the desired material on the surface of the substrate.
One PECVD process employed to deposit silicon carbide films involves the introduction of silane gas (SiH4) and methane gas (CH4) into a processing chamber where the gases react and form a film layer of silicon carbide on a substrate positioned in the chamber. In hydrogenated amorphous Sixe2x80x94C films, three elements are typically present; silicon, carbon, and hydrogen; forming Sixe2x80x94C bonds, Sixe2x80x94H bonds, and Cxe2x80x94H bonds. The ratio of Sixe2x80x94C bonds to other bonds is an important property of the film; a high ratio of Sixe2x80x94C bonds results in high film hardness, reduced surface roughness, and increased corrosion resistance. The ratio of Sixe2x80x94C bonds to other bonds is increased by raising the temperature of the wafer during the CVD process. However, the processing temperature is limited by melting points of integrated circuit structures an can-not be raised sufficiently to make a silicon carbide film having similar properties to a carbide film produced in a PVD process.
In light of the above, the present invention provides a CVD method and corresponding substrate processing system for depositing a silicon carbide film on a substrate at a satisfactory deposition rate while reducing the amount of hydrogen incorporated into the resulting film.
The present invention provides a silicon carbide (SiC) film having reduced hydrogen concentration. The SiC film is deposited on a substrate by introducing silane, methane gas, and a noble gas into a PECVD chamber and generating a plasma using RF power. The amount of hydrogen in the resulting silicon carbide film is inversely related to the amount of inert gas which is preferably helium or argon. The RF power is preferably a mixture of high and low frequency wherein the ratio of low frequency power to total power is less than about 0.6.